1. Technical Field
This invention relates to an engine control device for controlling an engine and, more specifically to an engine control device suitable for controlling an engine provided with a fuel injection device for injecting fuel.
2. Background Art
With the widespread use of fuel injection devices called injectors in recent years, the control of the fuel injection timing and the fuel injection amount, namely, the air-fuel ratio has become easy, which makes it possible to improve engine output and fuel consumption and to clean exhaust gas. As to the fuel injection timing, it is common that the phase state of a camshaft, the state of an intake valve, to be exact, is detected, and, based on the detected result, fuel is injected. However, a cam sensor for detecting the phase state of a camshaft, which is expensive and increases the size of a cylinder head, is difficult to employ in motorcycles or the like, in particular. To solve this problem, an engine control device adapted to detect the phase state of a crankshaft and an intake air pressure and, based on those, to detect the stroke state of a cylinder is conventionally known. Thus, it is possible to detect the stroke state of a cylinder without detecting the phase of a camshaft, so that it is possible to control the fuel injection timing based on the stroke state.
The stroke state can be detected based on variations in the engine rotational speed during one cycle. The engine rotational speed is highest in the expansion (explosion) stroke, followed by the exhaust stroke, intake stroke and compression stroke in that order. Thus, the stroke state can be detected from variations in the engine rotational speed and the phase of a crankshaft. A conventional engine control device is adapted to select the stroke detection based on variations in intake air pressure or stroke detection based on variations in the engine rotational speed according to the operating condition of the engine and detect a stroke by the selected method.
With the conventional engine control device, however, it is difficult to select an appropriate stroke detection method over the entire operating conditions of the engine and, in some cases, neither of the stroke detection methods is appropriate. Thus, the reliability of the detected stroke is low.
The present invention has been made to solve the above problem and it is an advantage of the present invention to provide an engine control device which can perform stroke detection with high reliability.